Journal of Histology and Cell Biology

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Abstract

What are stem cells? Stem cells are no differentiated cells that have the ability of proliferation, regeneration, conversion to differentiated cells and tissue production. Regeneration means that these cells have the ability of asymmetric division which one of the resulting cells remains as stem cell while another cell, which is called daughter cell, becomes one cell of germ layer. Stem cells may remain inactive for a long time till they enter cell division again

Editorial

What are stem cells? Stem cells are no differentiated cells that
have the ability of proliferation, regeneration, conversion to
differentiated cells and tissue production. Regeneration means
that these cells have the ability of asymmetric division which
one of the resulting cells remains as stem cell while another cell,
which is called daughter cell, becomes one cell of germ layer.
Stem cells may remain inactive for a long time till they enter
cell division again [1,2].

For the first time in 1981, researchers could isolate stem cells
from mouse embryos. More accurate studies on the biology of
mouse stem cells led to discovery of methods for separation of
stem cells from the human embryo in 1998 [3-5]. Stem cells
are divided into two groups: embryonic and adult stem cells.
Embryonic stem cells are derived from zygote cell which is
fertilized in vitro and usually is 4-5-day embryo that is in the
form of a hollow ball called blastocyst. Blastocyst is composed
of three parts: the trophoblast layer that is surrounding blastocyst,
a hollow cavity inside the blastocyst and inner cell mass that
changes to embryo. Since zygote cells can differentiate into
placenta and fetal cells, sometimes they are considered as the
only true totipotent stem cells. Because the inner cell mass of the
blastocyst does not have the ability to differentiate into placenta
cells, it is called the pluripotent cell. Non-differentiated cells
other than embryonic stem cells can be found in differentiated
cells of specific tissues after birth. These cells are called adult
or non-embryonic stem cells but more accurate word for them
is "somatic stem cells" because these cells also exist in children
and umbilical cord. They are divided into two main categories:
hematopoietic stem cells that can differentiate into blood cells
and mesenchymal stem cells that are less differentiated. Nose,
muscle, liver, skin, brain, retina and limbus of the eye are the
other sources of adult stem cells. One of the most important
advantages of adult stem cells over embryonic stem cells is
because of the fact that they can be obtained without the need
for destruction of embryo [6,7].

The pluripotent stem cell differentiates into the multipotent cell
of 3 different germ layers (ectoderm, mesoderm and endoderm
layer). The multipotent cell differentiates into unipotent cell of
a specific cell lineage within its germ layer [8]. If differentiation
process is successful, the resulting cells will be called as
progenitor cells or stem cell-like cells that have the capability
of regeneration [6]. Stem cell therapy has been evaluated
in various blood diseases (such as lymphoblastic leukemia,
myeloid leukemia, thalassemia, multiple myeloma, cell cycle
anemia).